Methods and Systems For Dynamic Calculation of Safety Stock Quantity

ABSTRACT

A computer-implemented method and system for calculating a safety stock quantity for several warehouses within an availability check during a delivery process of goods, wherein the safety stock quantity is representative of a quantity of products which is protected by the availability check, wherein the safety stock quantity is a combination of a predetermined safety stock quantity and a calculated safety stock quantity and the calculated safety stock quantity being a combination of the predetermined safety stock quantity, a percentage of the predetermined safety stock quantity, an expected demand quantity and a percentage of the expected demand quantity and wherein the safety stock quantity is calculated within the availability check using the predetermined safety stock quantity, the percentage of the predetermined safety stock quantity, the expected demand quantity and the percentage of the expected demand quantity for the respective delivery process of goods.

BACKGROUND OF THE INVENTION

The present invention relates generally to methods and systems formanaging inventory. More particularly, the present invention relates tomethods and systems for managing inventory by determining a safety stockquantity of goods within an availability check of a required quantity ofgoods.

Today, the success of a business company depends essentially on therequirement that customer demands on goods and/or services be fulfilledprecisely, cost-efficiently and in time. Therefore, many companies makeuse of a supply chain management system to control and optimize theirproduction and delivery processes.

Supply chain management may comprise the process of controlling the flowof goods, services, information and/or finances between the involvedparties such as manufactures, suppliers, wholesalers, retailers, andconsumers. This process may include, among others, order processing,information feedback, and timely delivering the ordered goods and/orservices.

One part of the supply chain management is the administration of theinventory in several warehouses, whereby the warehouses can be locatedwith each participant, e.g. manufacturer, dealer or middleman, which isinvolved in the supply chain. In this supply chain, a participant canact either as a supplier or as a customer.

Any inventory shortage in the supply chain could have negative effectson the efficiency of the business, including production delays, missedorder deadlines or disability to meet customers demand. Therefore, it isa basic task of the administration of the inventory to provide a minimuminventory, called the safety stock quantity, to prevent an inventoryshortage in the supply chain.

STATE OF THE ART

In current supply chain management systems the minimum inventory isimplemented as a static value for each product or product group. Thisvalue does not reflect any change in the customer's behaviour orseasonal fluctuation. Supply chain management systems which additionallyprovide an availability check of the required quantity of goods, usethis static value to determine the available quantity of goods.

SUMMARY OF THE INVENTION

In general, in one aspect, this invention provides acomputer-implemented method for calculating a protected safety stockquantity for several warehouses within an availability check during adelivery process of goods, whereby the safety stock quantity isrepresentative of a quantity of products which is protected by theavailability check, wherein

-   -   a safety stock indicator indicating whether or not a calculation        of the protected safety stock quantity has to be performed is        checked,    -   a safety stock parameter indicating how a calculation of the        protected safety stock quantity has to be performed is checked,    -   the protected safety stock quantity being a combination of at        least a predetermined safety stock quantity, a percentage of the        predetermined safety stock quantity, a expected demand quantity        and a percentage of the expected demand quantity,    -   the percentage of the predetermined safety stock quantity and        the percentage of the expected demand quantity being dependent        on a predetermined number of configurable characteristic values,    -   the percentage of the predetermined safety stock quantity and        the percentage of the expected demand quantity being        time-dependent, and    -   wherein the protected safety stock quantity is calculated within        the availability check using the predetermined safety stock        quantity, the percentage of the predetermined safety stock        quantity, the expected demand quantity and the percentage of the        expected demand quantity for the respective delivery process of        goods.

If a protected safety stock quantity has to be calculated, the inventivemethod provides the possibility to calculate the protected safety stockquantity in many different ways using one or more of the key figurespredetermined safety stock quantity, percentage of the predeterminedsafety stock quantity, expected demand quantity and percentage of theexpected demand quantity. The calculation may depend on severalparameters like customer type or product location.

Further embodiments of the invention can comprise the followingfeatures.

In one embodiment of the invention, there can be implemented thefollowing steps for calculating the protected safety stock quantity:

-   -   a first step of determining and evaluating the safety stock        indicator,    -   a second step of determining the predetermined safety stock        quantity, the percentage of the predetermined safety stock        quantity, the expected demand quantity and the percentage of the        expected demand quantity, if the evaluated safety stock        indicator indicates that a calculation of the safety stock        quantity has to be performed, and    -   a third step of determining the protected safety stock quantity.

A safety stock indicator indicates whether or not a protected safetystock quantity has to be calculated. Therefore, the inventive method maybe used also in systems where a calculation of a protected safety stockquantity it is not necessary.

If a calculation of a protected safety stock quantity is necessary,furthermore, the third step may provide two sub-steps for determiningthe protected safety stock quantity:

-   -   a first sub-step of evaluating the predetermined safety stock        quantity, the percentage of the predetermined safety stock        quantity, the expected demand quantity and the percentage of the        expected demand quantity, and    -   a second sub-step of calculating the protected safety stock        quantity.

The protected safety stock quantity is set to zero, if the evaluatedvalues predetermined safety stock quantity, percentage of thepredetermined safety stock quantity, expected demand quantity andpercentage of the expected demand quantity of the first sub-step are notvalid.

Using this equation, the inventive method can be used even if the keyfigures predetermined safety stock quantity, percentage of thepredetermined safety stock quantity, expected demand quantity andpercentage of the expected demand quantity are not maintained.

Further, the protected safety stock quantity is set to a combination ofthe evaluated values predetermined safety stock quantity, percentage ofthe predetermined safety stock quantity, expected demand quantity andpercentage of the expected demand quantity if the evaluated valuespredetermined safety stock quantity, percentage of the predeterminedsafety stock quantity, expected demand quantity and percentage of theexpected demand quantity of the first sub-step are valid.

Yet further, the protected safety stock quantity can be calculatedaccording to at least one of the following rules:

-   -   protected safety stock quantity is set to zero;    -   protected safety stock quantity is set to the predetermined        safety stock quantity;    -   protected safety stock quantity=predetermined safety stock        quantity*percentage of the predetermined safety stock        quantity+expected demand quantity*percentage of the expected        demand quantity;    -   protected safety stock quantity=predetermined safety stock        quantity+predetermined safety stock quantity*percentage of the        predetermined safety stock quantity+expected demand        quantity*percentage of the expected demand quantity;    -   protected safety stock quantity=predetermined safety stock        quantity+expected demand quantity.

One advantage is that the protected safety stock quantity may becalculated in many different ways depending on various requirements.

In a further embodiment, the predetermined safety stock quantity, theexpected demand quantity, the percentage of the predetermined safetystock quantity and the percentage of the expected demand quantity arestored in one or more time series which are used to estimate a demandforecast of required quantities of goods.

If the key figures predetermined safety stock quantity, expected demandquantity, percentage of the predetermined safety stock quantity andpercentage of the expected demand quantity are not maintained for aspecific time period, the method may use the available stored data toestimate a demand forecast of required quantities of goods. Furthermore,the key figures may vary over the time.

The time series are based on one or more characteristic values, wherebyone or more of the characteristic values can be summarized by usingcollective characteristic values and whereby the collectivecharacteristic values has at least one wildcard at the lower level ofthe characteristic values.

Using collective characteristic values reduces the number of time seriesand therefore the maintenance effort for the time series may be reduced.

Furthermore, there can be implemented a step of searching the timeseries for the required combination of characteristic values.

Further, the step of searching the time series may comprise

-   -   a first step of searching the time series for the required        combination of characteristic values, whereby the characteristic        value at the lower level will be substituted by a wildcard, and    -   a second step of performing the first step of searching, whereby        the characteristic value at the next higher level will be        additionally substituted by a wildcard, if the search in the        first step of searching fails.

In one embodiment, the data of the time series may be loaded from adatabase into a memory during the first access, whereby the memory ismanaged by the availability check process.

The availability check process reads the data of the time series fromthe memory for a further calculation of a safety stock quantity.

Reading the data for the time series from the memory, if the data is yetin the memory, leads to a better performance than reading the data fromthe database.

In a further embodiment, the invention provides an interface whichprovides methods for changing the configurable characteristic values toother computer-applications.

The interface further provides methods for changing the monthly demandquantities stored in the time series.

Other computer-applications, e.g. third party supply chain managementsystems, may access the time series for maintaining the time seriesusing several methods which are provided by the interface.

Furthermore, the invention comprises an apparatus comprising

-   -   a data storage device which stores a plurality of time series;    -   means which provides methods for changing a plurality of        configurable characteristic values to other        computer-applications;    -   means for calculating a protected safety stock quantity,        whereby the means for calculating a protected safety stock        quantity are adapted to perform the following steps:    -   determining and evaluating the safety stock indicator;    -   determining the predetermined safety stock quantity, the        percentage of the predetermined safety stock quantity, the        expected demand quantity and the percentage of the expected        demand quantity;    -   determining the protected safety stock quantity; and    -   searching the time series for a required combination of        characteristic values.

Furthermore, the invention comprises a computer-readable storage mediumcomprising computer-executable instructions for performing the methodaccording to the inventive methods, when loaded into a computer system.

Thus, the inventive method provides different ways to calculate aprotected safety stock quantity, whereby the calculation may depend onseveral key figures and on several program parameters e.g. customer typeor order type.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which constitute a part of this disclosure,illustrate various embodiments and aspects of the present invention and,together with the description, explain the principles of the invention.

In the drawings:

FIG. 1 illustrates a typical sourcing process of goods or productswithin a supply chain management system using an availability check anda determination of a safety stock quantity;

FIG. 2 illustrates an embodiment of a program flow of the presentinvention;

FIG. 3 illustrates the program flow of the determination of the keyfigures for the calculation of the safety stock quantity according toFIG. 2; and

FIG. 4 illustrates a more detailed embodiment of the calculation stepsaccording to FIG. 2.

DETAILED DESCRIPTION

In the following, the abbreviation PSQ is used for the term protectedsafety stock quantity and the abbreviation EDQ is used for the termexpected demand quantity.

FIG. 1 shows a typical sourcing process of products. A customer sends anorder 1 to a dealer. The order 1 may be an electronic order transmittedby email or a traditional order transmitted by mail. The order comprisesat least information about the required product and quantity. The dealerfeeds the data about the order 1 into the supply chain management system2 which processes this order 1 and provides information for the sourcingstep 6.

Within the supply chain management system 2, an availability check 3 isperformed as to whether the required product and quantity is availablein the warehouses 5.

For the availability check 3, the PSQ is taken into account. The PSQprotects a minimum of stock quantity, in order to guarantee a minimum ofstock quantity which will not be sold in normal cases. The PSQ isdetermined by the determination step 4.

FIG. 2 shows the inventive method of determining and calculating the PSQin a supply chain management environment. The method is implemented as acomputer program, whereby this computer program can be a part of theabove-mentioned supply chain management system. The method provides aninterface (not shown in this figure) for input and output parameters.One of the input parameters describes the required quantity of products.Another input parameter describes which product is concerned. One of theoutput parameter describes whether or not the PSQ was calculated.Another output parameter describes the PSQ itself if the PSQ wascalculated.

The method begins with step 10.

In step 20 the safety stock indicator is determined. The safety stockindicator indicates whether or not a calculation of the PSQ has to beperformed. In a preferred embodiment the safety stock indicator isstored in the product master data.

After the determination of the safety stock indicator, this indicator isevaluated in step 30. In this embodiment the safety stock indicator cantake the values YES or NO or the boolean values TRUE, or FALSE,respectively. If the safety stock indicator takes the value NO themethod goes to the step 100—no PSQ calculation will be performed. In thecase that the safety stock indicator takes the value YES, the methodgoes to step 40.

Step 40 performs the determination of several key figures which arerequired for the calculation of the PSQ. The key figures in thisembodiment are

-   -   a percentage of the predetermined safety stock quantity, and    -   a percentage of the expected demand.

Other embodiments can process more than these key figures. For theexpected demand a period specific demand quantity can be used, e.g. aweekly demand, a monthly demand or a quarterly demand. With thepercentages the weighting of the predetermined safety stock quantity andthe monthly demand during the calculation of the PSQ can be controlled.

These key figures depend on one or more characteristics, e.g. customertype and/or order type and may vary over the time. The key figures aremaintained as time series, whereby each meaningful combination ofcharacteristic values has its own time series. Each time seriescomprises one or more time periods whereby for each time period the keyfigures are maintained. In this embodiment the time period within a timeseries is set to ‘month’. Other time periods can be used for the periodspecific demand, e.g. week or quarter. A larger time period will reducethe maintenance effort for the time series. In this manner the keyfigures can vary from time period to time period.

The above mentioned safety stock indicator can additionally bemaintained in these time series. Thus, the decision whether or not acalculation of the PSQ has to be performed can depend also on the viewedtime period.

Step 40 is followed by step 50 which determines the quantities for thepredetermined safety stock quantity and the expected demand. In oneembodiment these key figures are stored in the product master data. Inother embodiments they could be stored together with the percentagevalues in the above mentioned time series. Thus, the calculation of thePSQ can depend also on the determined quantities.

After step 50 the step 60 is performed. In this step 60, the PSQ iscalculated. The PSQ calculated depends on the determined values of step40 and step 50. If the PSQ can be determined the above said outputparameter which describes the PSQ is set to the determined PSQ.

Finally the method ends with step 100.

FIG. 3 shows a detailed program flow of step 40 which determines the keyfigures percentage of the predetermined safety stock quantity andpercentage of the expected demand which are required for the calculationof the PSQ in this embodiment. These key figures are stored in timeseries.

In this embodiment it is not necessary to store time series for allpossible combinations of characteristic values. Several combinations ofcharacteristic values can be summarized by using collectivecharacteristics. This will lead to a reduced number of time series and asmaller data volume. Furthermore the effort for maintaining the timeseries can be reduced.

The first search step 41 comprises searching the time series byconsidering all characteristic values. In an example with threecharacteristic values CV1, CV2 and CV3 the characteristic combination is

-   -   {CV1, CV2, CV3}        -   (characteristic combination considering all characteristic            values)

If this characteristic combination, which is tested in step 42, is foundthe method goes to step 44. The step 44 reads the key figures stored inthe corresponding time series and takes it to calculate the PSQ. Thisstep 44 determines the key figures within the time series according tothe requested date. If the corresponding time series is empty or theviewed time period within the time series is not maintained, the valuespercentage of the predetermined safety stock quantity and percentage ofthe expected demand are set to zero.

If the characteristic combination is not found, the result of step 42 isNO and the method continues with step 43. In this step 43 thecharacteristic value of the lowest level will be substituted by awildcard. In the above example, this leads to the new characteristiccombination:

-   -   {CV1, CV2, *} (characteristic combination with one wildcard)

After the substitution in step 43 the step 40 is performed in arecursive manner using the new characteristic combination, until a timeseries for the characteristic combination is found. In each recursion,the next higher characteristic value will be substituted additionally bya wildcard. In the above example the next new characteristic combinationwithin the second recursion is:

-   -   {CV1, *, *} (characteristic combination with two wildcards)

If no characteristic combination is found, the PSQ is set to thepredetermined safety stock quantity. In another embodiment in this casethe PSQ can be set to zero.

In this embodiment the substitution begins with the lowest level andgoes to the next higher level by substituting additionally the nexthigher level by a wildcard:

-   -   {CV1, CV2, CV3}→{CV1, CV2, *}→{CV1, *, *}→{*, *, *}

In another embodiment, it could be meaningful to substitute only theviewed level by a wildcard:

-   -   {CV1, CV2, CV3}→{CV1, CV2, *}→{CV1, *, CV3}→{*, CV2, CV3}

Other rules for the substitution are also possible.

Step 40 is followed by a step 50 of determining the predetermined safetystock quantity and the expected demand.

FIG. 4 shows a more detailed program flow of step 60 shown in FIG. 2.This step 60 begins with step 61 evaluating the time series concerningthe percentage of the predetermined safety stock quantity and thepercentage of the expected demand. In the following step 62 theevaluated values from step 61 are checked if these are valid. Dependingon the result of step 62 the method goes to step 63 or step 70. Step 70evaluates the safety stock parameter, which controls how the calculationof the PSQ has to be performed.

In the following, the method calculates the PSQ according to one of thefollowing formulas:PSQ=0  (Formula 1)PSQ=predetermined safety stock quantity  (Formula 2)PSQ=predetermined safety stock quantity*percentage of the predeterminedsafety stock quantity+EDQ*percentage of the EDQ  (Formula 3)PSQ=predetermined safety stock quantity+predetermined safety stockquantity*percentage of the predetermined safety stockquantity+EDQ*percentage of the EDQ  (Formula 4)PSQ=predetermined safety stock quantity+EDQ  (Formula 5)

If the values checked in step 62 are valid the method continues withstep 63 by calculating the PSQ according to Formula 3.

The step 63 is followed by step 100 in FIG. 2.

If the values checked in step 62 are not valid, the method continueswith step 70 by evaluating the safety stock parameter. The followingstep 71 evaluates which value the safety stock parameter has. The safetystock parameter indicates whether and how the PSQ has to be calculated.If the safety stock parameter indicates that no PSQ has to be calculatedin the next step 72 the PSQ is set, according to Formula 1, to zero. Ifthe safety stock parameter indicates that a PSQ has to be calculated thefollowing step 73 calculates the PSQ according to Formula 5.

The steps 72 and 73 are followed by step 100 in FIG. 2.

In other embodiments, instead of Formula 3 the Formula 4 may be used,and instead of Formula 5 the Formula 2 may be used for calculating thePSQ.

The above said time series are used to estimate a demand forecast ofrequired quantities of goods or products. Therefore, in anotherembodiment, the program flow shown in FIG. 3 can be extended by anadditional step, which is not shown in FIG. 3, to performing a demandforecast if a corresponding time series was found but for the viewedtime period no EDQ is maintained in the time series. In a furtherembodiment the percentage of the predetermined safety stock quantity andthe percentage of the EDQ can be also calculated using a demandforecast.

In a preferred embodiment the data of the time series is loaded from adatabase into a memory during the first access. The memory in which thedata is loaded is managed by the inventive method. For furthercalculations of the PSQ the method may read the data of the time seriesdirectly from the memory, if the data is yet in the memory. Reading thedata for the time series from the memory leads to a better performancethan reading the data from the database.

In this embodiment the method provides an interface for changing theconfigurable characteristic values to other computer-applications. Theother computer-applications can be located on different computers,whereby the computers are connected by a communication network, e.g.LAN, WAN or Internet. This interface further provides methods forchanging the expected demand or the percentages stored in the timeseries. With this interface a collaborative planning process betweendifferent business companies can be implemented.

The present techniques can be implemented in digital electroniccircuitry, or in computer hardware, firmware, software, or incombinations of them. Apparatus of the invention can be implemented in acomputer program product tangibly embodied in a machine-readable storagedevice for execution by a programmable processor. Method steps accordingto the invention can be performed by a programmable processor executinga program of instructions to perform functions of the invention byoperating on the basis of input data, and by generating output data. Theinvention may be implemented in one or several computer programs thatare executable in a programmable system, which includes at least oneprogrammable processor coupled to receive data from, and transmit datato, a storage system, at least one input device, and at least one outputdevice, respectively. Computer programs may be implemented in ahigh-level or object-oriented programming language, and/or in assemblyor machine code. The language or code can be a compiled or interpretedlanguage or code. Processors may include general and special purposemicroprocessors. A processor receives instructions and data frommemories, in particular from read-only memories and/or random accessmemories. A computer may include one or more mass storage devices forstoring data; such devices may include magnetic disks, such as internalhard disks and removable disks; magneto-optical disks; and opticaldisks. Storage devices suitable for tangibly embodying computer programinstructions and data include all forms of non-volatile memory,including by way of example semiconductor memory devices, such as EPROM,EEPROM, and flash memory devices; magnetic disks such as internal harddisks and removable disks; magneto-optical disks; and CD-ROM disks. Anyof the foregoing can be supplemented by or incorporated in ASICs(application-specific integrated circuits).

The computer systems or distributed computer networks as mentioned abovemay be used, for example, for producing goods, delivering parts forassembling products, controlling technical or economical processes, orimplementing telecommunication activities.

To provide for interaction with a user, the invention can be implementedon a computer system having a display device such as a monitor or LCDscreen for displaying information to the user and a keyboard and apointing device such as a mouse or a trackball by which the user canprovide input to the computer system. The computer system can beprogrammed to provide a graphical or text user interface through whichcomputer programs interact with users.

A computer may include a processor, memory coupled to the processor, ahard drive controller, a video controller and an input/output controllercoupled to the processor by a processor bus. The hard drive controlleris coupled to a hard disk drive suitable for storing executable computerprograms, including programs embodying the present technique. The I/Ocontroller is coupled by means of an I/O bus to an I/O interface. TheI/O interface receives and transmits in analogue or digital form over atleast one communication link. Such a communication link may be a seriallink, a parallel link, local area network, or wireless link (e.g. an RFcommunication link). A display is coupled to an interface, which iscoupled to an I/O bus. A keyboard and pointing device are also coupledto the I/O bus. Alternatively, separate buses may be used for thekeyboard pointing device and I/O interface.

1. A computer-implemented method for calculating a protected safetystock quantity for several warehouses within an availability checkduring a delivery process of goods, whereby the protected safety stockquantity is representative of a quantity of products which is protectedby the availability check, wherein a safety stock indicator indicatingwhether or not a calculation of the protected safety stock quantity hasto be performed is checked, a safety stock parameter indicating how acalculation of the protected safety stock quantity has to be performedis checked, the safety stock quantity being a combination of at least apredetermined safety stock quantity, a percentage of the predeterminedsafety stock quantity, a expected demand quantity and a percentage ofthe expected demand quantity, the percentage of the predetermined safetystock quantity and the percentage of the expected demand quantity beingdependent on a predetermined number of configurable characteristicvalues, the percentage of the predetermined safety stock quantity andthe percentage of the expected demand quantity being time-dependent, andwherein the protected safety stock quantity is calculated within theavailability check using the predetermined safety stock quantity, thepercentage of the predetermined safety stock quantity, the expecteddemand quantity and the percentage of the expected demand quantity forthe respective delivery process of goods.
 2. The method of claim 1,wherein the calculation of the protected safety stock quantitycomprising the following steps: a first step of determining andevaluating the safety stock indicator, a second step of determining thepredetermined safety stock quantity, the percentage of the predeterminedsafety stock quantity, the expected demand quantity and the percentageof the expected demand quantity, if the evaluated safety stock indicatorindicates that a calculation of the safety stock quantity has to beperformed, and a third step of determining the protected safety stockquantity.
 3. The method of claim 2, wherein the third step furthercomprising the following steps: a first sub-step of evaluating thepredetermined safety stock quantity, the percentage of the predeterminedsafety stock quantity, the expected demand quantity and the percentageof the expected demand quantity, and a second sub-step of calculatingthe protected safety stock quantity.
 4. The method of claim 3, whereinthe protected safety stock quantity is set to zero if the evaluatedvalues predetermined safety stock quantity, percentage of thepredetermined safety stock quantity, expected demand quantity andpercentage of the expected demand quantity of the first sub-step are notvalid.
 5. The method of claim 3, wherein the protected safety stockquantity is set to a combination of the evaluated values predeterminedsafety stock quantity, percentage of the predetermined safety stockquantity, expected demand quantity and percentage of the expected demandquantity if the evaluated values predetermined safety stock quantity,percentage of the predetermined safety stock quantity, expected demandquantity and percentage of the expected demand quantity of the firstsub-step are valid.
 6. The method of claim 5, wherein the protectedsafety stock quantity being calculated according to at least one of thefollowing rules: protected safety stock quantity is set to zeroprotected safety stock quantity is set to the predetermined safety stockquantity protected safety stock quantity=predetermined safety stockquantity*percentage of the predetermined safety stock quantity+expecteddemand quantity*percentage of the expected demand quantity, protectedsafety stock quantity=predetermined safety stock quantity+predeterminedsafety stock quantity*percentage of the predetermined safety stockquantity+expected demand quantity*percentage of the expected demandquantity, protected safety stock quantity=predetermined safety stockquantity+expected demand quantity.
 7. The method of one of the precedingclaims, wherein the predetermined safety stock quantity, the expecteddemand quantity, the percentage of the predetermined safety stockquantity and the percentage of the expected demand quantity are storedin one or more time series which are used to estimate a demand forecastof required quantities of goods.
 8. The method of claim 7, wherein thetime series are based on one or more characteristic values, whereby oneor more of the characteristic values can be summarized by usingcollective characteristic values and whereby the collectivecharacteristic values has at least one wildcard at the lower level ofthe characteristic values.
 9. The method of one of the preceding claims,wherein the determination of the predetermined safety stock quantity,the percentage of the predetermined safety stock quantity, the expecteddemand quantity and the percentage of the expected demand quantitystored in the said time series comprises a step of searching the timeseries for the required combination of characteristic values.
 10. Themethod of claim 9, further comprising a first step of searching the timeseries for the required combination of characteristic values, wherebythe characteristic value at the lower level will be substituted by awildcard, if the step of claim 9 fails, and a second step of performingthe first step, whereby the characteristic value at the next higherlevel will be additionally substituted by a wildcard, if the search inthe first step fails.
 11. The method of one of the preceding claims,wherein the data of the time series is loaded from a database into amemory during the first access, whereby the memory is managed by theavailability check process.
 12. The method of claim 11, wherein theavailability check process reads the data of the time series from thememory for a further calculation of a safety stock quantity.
 13. Themethod of one of the preceding claims, further comprising an interfacewhich provides methods for changing the configurable characteristicvalues to other computer-applications.
 14. The method of claim 13,wherein the interface further provides methods for changing the monthlydemand quantities stored in the time series.
 15. An apparatus comprisinga data storage device which stores a plurality of time series; meanswhich provides methods for changing a plurality of configurablecharacteristic values to other computer-applications; means forcalculating a protected safety stock quantity; wherein the means forcalculating a protected safety stock quantity are adapted to perform thefollowing steps: determining and evaluating the safety stock indicator;determining the predetermined safety stock quantity, the percentage ofthe predetermined safety stock quantity, the expected demand quantityand the percentage of the expected demand quantity; determining theprotected safety stock quantity; and searching the time series for arequired combination of characteristic values.
 16. A computer-readablemedium comprising computer-executable instructions for performing themethod according to one of claims 1 to 14, when loaded into a computersystem.